Treatment of liquids containing tar acids



Aug, 1, 1933, F. w. sPERR, JR., Er AL TREATMENTOF LIQUIDS CONTAINING TAR ACIDS Filed Jan. 9, 1931 DILDW. NL'WUQS 411km/ MMTVMCL FOI def/bk JIZL' Mmmm M030] wm@ UTPWDIO .I WMWTL Patented Aug. l, 1933` 1,920,604 y zTREATMENT oF-LIQUIDS coNTAININGTAR l Acms l Vlflrederick W. Sperr, Jr., and Joseph A. Shaw,v

Pittsburgh, Pa., `assignors to The Kappers Company of Delaware, a Corporation of Del-` aware 4 Application January 9, 1931. Serial No. 507,618Y zo claims. `(C1. 26o-154') Our invention relates to the treatment of liquids containing tar acids, and especially to the treatment of liquor produced'in-the manufacture and purification Vof fuel gas for thevremovall 5 of tar acids therefrom. A,

In many localities the discharge of industrial eilluents .and other waste liquors contantinated with tar acids into Water courses,sewers, etc., is prohibited. Consequently,A many indus'- tries have been confrontedV with a4 seriouslproblem regarding disposal of elluentscontaminated .with phenols (tar acids) including phenol, cresol, and their homologues. Y y f Q This problem has been especially acute in the manufactured gas industryfwhere it is j Ygeneral practice to cool and .partially condensethe crude` gas fromcoke ovens, retorts, etc,, to remove tar,

and ammonia. During this condensation am-v moniacal gas liquor is producedin they presence 2 of tar, andthe liquor is contaminated with water soluble portions` of the tar, especially the tar acids, to an extent dependent upon the concentration ofvphenols in the tar-y the system of condensation, the temperature to which vthe gas is cooled, etc. 1 1 1 The amount of ammoniacal liquor obtained also varies according to the process of condensation and ammonia recovery use. In the direct process of ammoniarecovery Ywhich is widely 3 l used in this country, gas'liquor production generally amounts to about twenty gallons per ton of coal carbonized, and this liquor usually contains from two to live grams of tar acids per liter. In the indirect process of ammonia,V recovery,` a much greater volume of liquor 4is produced."

Y When'gas liquor is distilled in the. usual manner for recovery of ammonia, the major portion,

of the tar acids remains in theliquor and is discharged in` the ammoniaystill 'waste.. At least L0 a' portion of these tar acids is fixed in the form of salts such as` calcium phenolate when discharged from the still, but When such'compounds get into streams the tar acids are liberated by the action or carbon Vdioxide kand other acidic 5 constituents of the water. If this'water is sub- Vsequently'chlorinated in the course of .purification'forV municipal consumption, as often happens, an'unpleasant taste may result, and it ,is

0 this nuisancethat regulations'prohibiting-phenolic pollution of streams are intended toprev'ent.

In' many instances it is unfeasible or impossible to dispose of the effluent from gas plant` ammonia stills Without allowing at least part of it to get into water courses. The unpleasant consequences of such an occurrence are accentuated by the fact thatlarge gas plants, coke-oven plants, and the like, are frequentlylocated near centers of populationv Where it is customaryrto obtain the municipal Water suppliesv fromV streams i Y Y To eliminate this 4nuisance itisV frequently desirable to remove tar 'acids prior to the dis-` charge ofwthe still waste.; To. accomplishl Ythis Y removal, several processes of dephenolization have been developed. AOf these the most successful is the Vapor recirculation process described by Joseph A. Shawin acopending application'Serial No. 230,570f1led November 2, 1927, (Case No. 103). l l, In that process, ammoniacal gas liquorisfdistilled'for removal of freeammonia inthe usual manner. The hot liquor is thenscrubbed with a` v countercurrentof recirculated-gas, such asgair, whichis saturated with steam and at a temperature' near the boiling point oftheV liquor,fand 75 v which removes tar` acids from the liquor. 'The dephenolized liquor is then mixedpwith lime and distilled to recover the previously xed ammonia, v

and the still waste may be discharged asdesired,` Y y substantially without danger ofphenolic pollution of streams. 1

The vapor or saturated ga'sservesto transfer. Y the phenols removed from the liquor in the strip! ping'stage of the dephenolization process toa suitable absorbing agent, such as',caustic,sodaV solution, with `which theenriched'vapor is contactedin the absorbing'stage of the process.` The caustic reacts with the tar acids to formmsodium phenolate and analogous compounds.' The puried vapor `is recirculated to dephenolize fur ther quantities of liquor and the phenolate ,solution'is withdrawn and treated for recovery `of phenolsor otherwise disposed of, Freshg'caustic f solution is supplied to replace the Withdrawn phenolate. 'Y f' In the application of this process on a'com` mercial scale we have made certain modications resulting in anximprovement inl-the process and apparatusl for removing tar acids fromyliquids containing them, which is an'v object of Aour invention. j l Anotherobject ofour'invention isfto yprovide a process of andappa'ratus for removing tar"acids from liquids containing them more Vefficiently 105V than has been possible by means of .prior 1vJ rocesses and apparatus. y Y

` A further object o f ourinventionis-to pro- `videa process of andfapparatus for removing tar q acids from liquids )containing them more eco- 110 Y nomically .than-has been possible. by means Aof prior processes and apparatus. 4 l Y Our invention hasA for furtherv objects such other advantages andresultsvas are-,found Vto obscribedand claimed.y i y j We haye foun'dthat preventing the` carbonation ofthe Vcaustic which absorbs tar acids from; the recirculating vapor, and whichsometixnesbetain in the process and apparatus hereinafter ide-fy l j" l V comescarbonated `due to the presenceof,l icares v roo

Yvfntage'ous results are process of land apparatus sorbing-'stage of the dephenolizer into a single towerresults in saving heatand` vground space.

We have found that absorbing tar acids from theY recirculating vapor in a-plurality of stages including one stage or more in which the vapor is contacted with a recirculated absorbent'and a stage in which it is contacted with intermittently supplied fresh absorbent results in especially eiiicient and economicaloperation,'particularly with respect-to the purification of the vapor and the conversion of the caustic to phenolate.

` We have found that increased economy and i-ifhciency'result' from the rautn'natic regulation of temperature inthe dephenolizing tower, and thatv control of the'rate vof vapor recirculation and a suitable system of Yvents on the hot liquor and solution Vlines are also beneficialn Wehave found also that the substitution of a Substantially oxygen 'freegaa such asia-'cokeoven gas, for air in the recirculating vapor minimizes corrosion and is especially economical ,thefgas is `free from carbon dioxide. Y We have found furtherlthat all of these adobtained in theimproved n for d'ephenolization con- `s` titfuting our present invention. y We now describe with reference tothe accompanying" drawing a'prefer'red method of practicing lour improved process ci dephenolizing liquids gas liquor "condensed fromv containing tar acids, especially'the ammoniacal coke-oven gas and the like, and a preferred type of apparatus therefor. In thedrawing, f Thesingle vfigure-is a partially diagrammatic View "partly" in elevationand partly in vertical iser'ztiofn, of apparatus suitable for the practice 'of our present invention.V

mr'no Yiacal as liquor containing freel and fixed ammonia, ltar acids and other impurities Asuch as CO, B2S, andthe like enters a free ammonia still 1 through a pipe 2. Tlie`-still l is part of an installation Yof the usual typefor recovering ammonia liquor, saidinstallation a `linie mixing cham-j ber' and'a fixed ammonia still 4'. j.

The liquor passes downwardly through the free 'stili `1 in `countercurrent iiow with steam or other hot vapor which removes free ammoniaand other volatile ,constituents from the liquor and carries .them out. of .the still througha vaDOlline 6. The hot Vliquor then passes from the bottom of the Y free still 1 through a sealed oitake line '7 into an, ammonia liquor surge tank 8. Temperatures arefadjus'ted'by controlling the! rate 'at v'which still and/or dephlegmating 'the 'vapors leaving through `pipe A6lv so that 4substantially vall* of the free ammonial is removed butl at least the major portion ofthe 'tfarfacids 'remains in ythe liquor'discharged-to tank 8.

- vA l1'0` withdraws liquor Vfrom the tankZ 8 through -a pipe 1l and delivers it through pipes 11i-and 14 and sprays 15 lor other suitable distributing devices into the v'ammonia liquor-sec'- ftion vor stripping section 1 7 of v a dephenolizing to'fwr 20. The liquor'isV distributed bythe sprays eoversuitable contact material such `aswoofden hurdles or spiral tile packing 211 with which `the 'section 1'7 ispacked and passes downwardly over lthispacking. During repassage the Anot fnquor isintim'ately"contacted with acountercurr'ent of vl`hot' vapor or saturated gas ,which removes vtar 4steam brought in through pipe 29.

' is mixed with lime, or other suitable alkalinematerial introduced through a pipe 28, by means'of liberates the xed ammonia and the liquor Voverflows from the lime mixing chamber through a pipe to the xed still 4. In this still the liquor is subjected to further distillation with steam introduced .through a pipe 32 for removal of the previously fixed ammonia, and' vapors pass from the fixed still 4 into the free still lthrough a 'pipe 34.

The distilled liquor, or still waste, is discharged rfrom the bottom of the fixed still 4 throughs,

pipe 35 and a trap 36 substantially free from ammonia `and taracids, and enters a still'w'aste settling sump or basin 40 from which stilllwas'te is withdrawn r.to be disposed of as desired. v

The stripping stage or `section 17 of the .dephenolizeri-ZOis preferably located-at the top of a tower which also contains the absorbing stage. In the present instance, the absorbing stage consists of two recirculating absorbent sections 41 and 42,' and a or shot section 43. Fresh caustic solution, or

other suitable absorbent, is 'withdrawn from a fresh absorbent rsection :mixing tank 45rby a pump 46 controlled by an automaticVv regulating meter f4? and delivered, preferably intermittently, through a pipe 43 and sprays '49 'overcont'act material such as steel lathe turnings 51 vwith which the shotl section 43 of the tower'20`is packed. i

The caustic isiheld in the path ofthe recirculating `vap`or by the contact material and completes the purification of the vapor from tar acids.

lll

The thereby purified vapor passes lthrough a pipe 53 into the strippingv 'section l'l of the idephenolizer, where it removes/tar acids from ammonia liquor as described hereinabove.

`The fresh caustic drips down through the conu tact material 51 and through ak connectingpipe 54A intofthe upper recirculating section 42 vof the dephenolizer.

'Caustic solution is recirculated over this section byapump 55 whichdeliver'sthe A solution ,through pipes 56 `vand Y5 '7 and sprays onto'the'` contact material V59 with which'rthis section ispacked.V Below thesprays 56 thefrecirculatedcaustic is mixed vwith the' fresh caustic coming. down through the 'pipe' 54, `and"isf-thereby Vpartially refreshedl The caustic then passesV downwardly throughV ythe contact `materialand collects inia well 6'1 at the bottom of section 42, from which it returns vthrough a pipe 63 to Athe pump 55 for recirculation. l Y

The fresh caustic entering' the pipe 54 causes the well 61 to overi'iow, and the this'section 'through overflowing solutionv of caustic and phenolateVV passesA downwardly to the llower recirculating section 4l. Thecaus-i tic-phenolate solution'is recirculated 'over this througha pip'e`67 and sprays 68 onto 'the'contact material 70 withwhich 'this section 41 i's packed.

Below the sprays 63 `this recirculating. solution is mixed with the solution overflowing `fromwell through connecting pipe j j Y section by a 'pump whichdelivers the solution 61, 'and the Ycombined Vsolution passes down V through the packing 'YO'andcollects in a well'oxl sump rIlfat'thebottom of the tower. The phenoliate solutionovlerflows vfrom the well and passes through a, sealed and vented discharge pipe 73 intoa phenolate storage tank 75. l v

Vapor or saturated gas is recirculated through` the dephenolizer and the downcomer23 `by a blower 78 or other suitablebmeans, at -a rate which may be controlled by a butteriiy valve or damper 79 in the downcomer 23.

VThe enriched or fouled vapor leaving the a monia liquor section 17 at the top of the dephenolizer passes downwardly through the downcomer 23 and is recirculated into thelower section 41 of the tower. In this section a portion of the Vtar acids is removed from thefgaswhich then passes through pipe into the second or upper recirculating section 42 where arfurther portion of the tar acids isremoved by recirculated caustic-phenclate solution. The gas thenl passes .l

through pipei54 into the shot section-` 43 in which itspurification from tar acids is completed and the purified or lean vapor re-enters the scrubbing section 17 through pipe 53. I

This vapor may consist of. any suitable-inert gas such as air, ammonia, or the like, vsaturated with Water vapor. However, Wehave foundthat benecial results are obtained if a` substantially oxygen-free gas such as=cokeovengas is used.'

Coke-oven gas is supplied through a Vpipe 81, a purifieror rpuriiiers82 and pipes 83 and 84tofa convenient point in the system, such as a point in the vapor line before or after the blower 78.

The admission of gas to the 'system' iswciontrolled by a pressure regulatingvalve `vifljiich only allows gas to enter when thepressurein the systemA is below normal. The purifiers 82 are j nlled with lime or other suitable material which serves to remove carbon dioxide and other acidic yconstituents from the gas'and thus prevents the carbonation of the caustic vby absorption of carbon ydioxide introduced into the recirculating i gj vapor fromthis source. It is Vimportant that such absorption be prevented, ascarbonationof the caustic results in decreased efliciencyvof .tar acid absorption and increasedcon'smption of caustic, making' the processV moreexpensive Vas 1 Another troublesome source of` acidic impurities vis the ammonia liquor itself, from which CO2 and the likeare usuallynearly but not complete# ly removed in the free ammonia still 1. j We have found that the consumption Aof caustic 'resulting fromv absorption of carbon dioxide from this sourcecan be prevented by adding substances which fix the COz'either to the liquoritself or to the recirculating caustic." f

Examples of suitable ,i'ixing materials for this purpose are lime, magnesia, and solublesalts of calcium, barium7 and otherbases which form insoluble carbonates.l A convenient and cheap i supply of material of this nature is available in the still Waste, which contains considerable quantities of calcium chloride, and Whichisordnari-v ly wasted. j

' We have found. that by adding the Yproper` amount of clarified still waste tothe ammonia liquor beforeit enters the dephenolizer, the removal. of CO2 in the stripping. section and its transfer to the absorbing section, resulting incarbonation of the caustic, are readily prevented. To acc-empiish this, @armed Suu wasteis withdrawn from the settling sump 40 through a pipe 87 byapunip 88 and delivered through a pipe 89v to-a tankl90. Alternatively, milk of lime, salts of Vcalciumiand other alkaline earthmetalsfad the like, may be introduced from Asome othersource 88 and delivered to the tank-90.

through apipe 91 to the inlet side of the yp'mrnpl `The `tank 90 is V,preferably ventedto equalize its Ypressure with that in the surge tank 8 by a pipe 92 connecting tanks-90 and -above the levels of a pipe 93, `Venting the tank back tothe still 1, or a pipe94 whereby thetank is vented to the de phenolizer 2 0, and lpipe 92 may conveniently be f the liquids therein. The tank 8 isvented to prevent vaporbinding in-.pipe 1 1 Vand pump 10 by the insolublefcarbonate before the` liquor goes to the dep'henolizer. This is accomplished by a .filter 97 to which the liquor Ais delivered b y pump 10 and from which it passes through pipe 98 into pipe 14 and` thence to the dephenolizer; Thek filter also removes pitch and other solids which might tion 17 of the dephenolizer. i v

In some instances it may be preferable to vprevent carbonation of the caustic by fixing the CO2 in the form of insoluble'carbonates after admission to the dephenolizer. We havefound that this maybe satisfactorily accomplished by adding milk `of lime` or other suitable material, such as asolution of an alkali earth metalsalt, ytof'the caustic in the ,absorbing section'of the dephenolizer. f i 1 This procedure has the advantage of fixing CO2 tend to clog the packing 21 in thestripping sec-.-

from other sources than the; liquor-e. g., from lthe `recirculated gas. ,Furthermore if lime `used as theiixingagentit recausticizes the alkali 'ca rbonates usually, present in .thexcaustic due to absorption of CO2 fromy the V'airorfto incomplete ,120.

purification in the course of manufacture.

,The fixing material `maybe supplied in a .variety of ways to the absorbing sectionof thedephenolizer, as by mixing itwith the fresh caustic solution supplied' to the shot sectionl 43,ibut we' have found it to be advantageous to make the adf' ditions to the recirculated caustic, preferably in the upper'recirculating `section 42. `This is conf veniently accomplished `by Ymeans of a tank 1 00 to which the fixing solution orgy suspension is i supplied through a pipe 101. 'I heqtank '100 is preferably vented tothe dephenolizer, as by a pipe l other suitableheatingfmeans if desired. l

` The vfixing solution orl suspension `passes from tank 100 through apipe 103 into pipe 57, and enters the section 42'of the dephenolizerwith ltheref 102, andinay'be provided'with a. steam coil or circulated caustic-phenolate solution.v `In passing. down through the packing in section ,42, overl which it is recirculated, andy in section 41 to whichit overiiows from the wellf61 in section 42, the lime or other iixingagentreacts with COzl carried by the'recirculated-vapor and removes` it jfrom the vapor; Contamination of .'th'e fresh caustic `in the shot section 43 with CO2 is thereby prevented, which makesjit possible to .remove tracesof ltar .acids remainingin the vaporentering the shot section with-a comparatively small amount of fresh caustic. yThe Vratez itvvhichthe fixing agent is addedto the caustic depends on what other steps are taken tovprevent carbonation. ,HIf no 'other provision against carbonation ismade, sufficient rlinie or similar material should` beadded to the recirculated absorbent to "combine with CO2 introduced into the system from the ammonia liquor and the gas, and tocausticiz'e tained'infthe fresh caustic. ,l Y

When the liquor and/or gas are treated with lime or thelike, as described above-"before admise jsion to the dephenolizer, the amount of xing Vmaterial added to the absorbent' may be 'correspondingly decreased. Any of lthese -three methods of fixing CO2 toprevent carbonation of the caustic maybe usedalone, or in combination with oneor both of the others.

VAlthough CO2' is generally and consequently the most troublesome contaminator of the alkaline absorbent, other normally gaseous acidic constituents of ammonia liquor, such aslIzS, HCN, and .the like, ,are similar to CO2k in theireffect onlrcaustic consumption and tar acid absorption. Consequently whathas been said hereinabove regarding the desirability Aof fixing CO2 to prevent contamination of the abfsorbent applies also to these otherv acidic compoundswhen they are present in the liquor. Their plying heat to the Wells 6l Vand/or '71 in the rre circulating sectionsA 42" and V'sil` respectively `by ,345.; steam coils orvother suitable heating means.k ToY xation in the Yform of compounds which areV insoluble and/ or have substantially no vapor pressure is accomplished simultaneously with the fixa'- tion of CO2 by the methods described hereinabove.

The temperature maintained in the dephenolizer` is-a very important factor in the elciency of the process, and the best. results are generally obtained when the dephenolized liquor leaves the stripping section 17 at a temperature near but slightly belov/ its boiling point.v Complete insulation of the tower and piping is important in keeping this temperature approximately constant, but is notin itself sufficient. Y

We have found that the desired temperaturesthroughout the system canbemaintained by supfsimplify operation, the amount of heat supplied is automatically controlled, as bya temperature Y regulator 105 iwhich controls the rate at 'which j, opened allowing steam to enter and pass through v steam is supplied to a coil 106 inthe vvellz'llVVV through. pipe 107.

Theregulator 105 forms no part of thepresent invention.Y It is set to maintain 'the desired ternperature in the well 71v When the temperatureV `falls belovv that point,v a valve is automatically the coil-166 until thedesired temperature is reached, andthe valve is then automatically closed.v Afsirnilar regulatoris preferably used to regulate theY admission of steam to coil 109 in welll. Y The vapor ratio-that is',,the numberr of volumes of .vapor circulated per volume of vliquor treated;-

' also'has an important bearing on the efficiencyV of lephenoiizati.on.L In general, other conditions being equal, the higher the vapor rate the higher x,the efliciency up to aV certain optimum ratio,

which isusually between 1500' and 4000,*but is sometimes higher.` Above this optimum ratio, the eiiiciency'increases vapor rates.

i'sfessential thatv the blower 73 -be largeV enough to provide vapor recirculation .atrthe optimum rate when the maximum quantity of vliquor is beingltreated. However, the rateY at 'which liquor Vis,supplied for treatment may be and oftenis any carbonates `con'-V uie" moet pientifuiY more slowly with increased' To ensure the maximum efficiency obtainable, it

less menthe' maximum. f When'this oecurs; the

vapor ratio 'becomes higher than-necessary, re#V sultingin excessivepower-consumption; Wehhave found that a means of throttling the blower to make the rate of vapor recirculation proportional to the liquor rate, 'suchas thebutterfly valvev or damper 79 in the vapor downcomer 23, is effec-U tive inpreventingunnecessary power consumption.vk 'l As' has Ybeen stated previously, itis essentialto the economy" o f our dephenolization process that the vapor or saturatedgas bejrecirculated, which involve's-'removing tar acids from/ajlarge volume vof vapor on each Acycle lthrough the system." For example, in` a plantmcarbonizing 1000 tons of coal perday about 120,000 gallons" of ammonia liquor are produced, or about2700 cu. it. With a vapor ratio vof 3000, dephenolization of thisliquoririf" volves purifying 8.4 million 'culrft'yof vapor 'per day, or about340Mcu-ft, per hr. 1

lf the tar acid content ofthe gas' liquoris 3 K gramsper liter (g. p. 1.) lwhich is reduced to .05

g. p. l. or less, the amount of tar` acidremoved is,v 2.95 g. p. l. or' about 11 gramspergallon of liquor,

Vmaking a total of 220,000grams or about 484`1bs.

per'day. Assuming this to `be 'entirely phenol, the amount vof caustic soda theoretically Vrequired toV react with, it to form phenolate is 206vlbs; If twicethis amount is"` actually used to ensure lthorough removal of tar acidsffrom the vapor,

theftotal arnountf of caustic soda supplied yis 412 lbsrper day,oz1 a drybasis.' Y Y F .-This caustic is supplied to the absorbing section of the dephenolizerin the formof a solution preferably containing about 10%r NaOH, although We have found that other solution strengths, such as Thisfrom 3%' `to 25% give satisfactory results. 10% Acaustic' solution, amounting to about `V480' gallonsper day, lor 20 gallons per hl, must be so intimately contacted with the'vapor that the vaporis very completely puried fromY tar acids.

,l'jorexample assuming Ythatjthe vapor is so'` perfectly contacted Withthe liquor in the stripping section that 'phenols'in the Adeplfienolized liquor' leaving this ysection are Ain equilibrium with phenolsin the vapor entering, the tar acid content of thisv vapor '(When condensed) `must be not more Vthan about twice the desired tar'acid con? tentoftle dephenolizedfliquori, In practice this ratio must usually be lower than 2.] As itis gerierally desirable yto have the tar acid content of the -dephe'nolized liquor' a's lo'W as possible, itisv preferable to purifythe recirculated vapor to a tar acid-content notexceeding 50 parts per million' by Weight When condensed'. It is obviouslyirnpractical to effectively Contact 340 cu. ft. offlovving gas orjvap'orrwith 20'V gallons of fresh absorbent in ascrubber of the usual type. To accomplish this We have employed' turnings 5`1or other contact material with whichVV Y Athe shotsection 4 3' ofthe dephenolizer ispacked.V

The extensive caustic-coated surface thereby exposedfto thev vapor Visveryeffective i'nremovin'g -teral 70 in Section 41.

gallonshot might be delivered every two hours,pr

or a twenty gallon shot every hour, or a ten gallon shot every half hour, etc.

The-limiting frequencies are that at which shots are made just frequently enough tokeep a coating of unconverted'causticlon the Contact material, and thatat which the amount of liquid 'delivered' per shot is just suicient to ensure good distribution across the upper Ysurface of the contact material. This upper llimit is in turn dependent upon the concentration of the solution employed.

We have found that by'means of our improved apparatus for dephenolization the recirculated vapor can be purified from tar acids to such an extent that adequate' dephenolization ofthe am-4 monia liquor isachieved, and the conversion of caustic to phenolateis high. For example, in

large scale operation we have obtainedbetter than 95% removal of tar acids from the liquorv when thecaustic was more than 70% converted to phenolate before discharge to storage.: The recirculating sections 41 and 42v are important in obtaining this high conversion and the consequent Ysaving of caustic. K Y

As the vapor passes through the two recirculating absorbent sections followed by a fresh absorbent shot section, the decreasing tar acid content of the vapor undergoing purification and the consequent increasing diiculty of further removal therefromv are compensated for by the decreased extent or percentage of the conversion to phenolate of the `caustic with which the vapor is contasted, so that the purication is progressive and veryc'omplete. Also a major portion of the tar acid is absorbed in the lower section 4l, from which phenolate is discharged to storage, so that the percentage conversion can become very high there without interfering with the ultimate purication of the Vapor. j

In some` instances, oneror both of the recirculating sections 414 and 42 maybe omitted, or

solution may be recirculated over both sections in series instead of in parallel. WhenV a recirculating sectionv (or sections)V is omitted, the A .lent in effect to using only one section with greater depth of contact material, only one recirculating pump is used. By installing suitable connecting pipes, such as a pipe 112 connecting the inlets of pumps Hand 66 and a pipe 113 connecting the discharge pipes 56 and 67, either of these pumps is made available for this service.

The caustic-phenolate solution is'then withdrawn from the lower Well471 by pump 66 or 55' and l delivered through pipesx67 `and 113, or

` through pipe 56, to pipe 57, through which it enters section 42. The absorbent is distributed bythe sprays 58 over the contact material 59, through which it passes countercurrently to the flow of vapor, and collects in well 61.

vFrom 'this well it overows, passing doWnward through passage onto the contact ma- AAfter passing down through this packing it collects in the lower well '71 for recirculation, and excess solution overfiows through the sealed vented discharge pipe 73 tothe phenolate storage tank 75.

lto cover in the claims such modifications'asare `an alkaline absorbent for taracids and prevent- 'carbon dioxide entering the systemgto form-an 5" Whatever the number of absorbing sections in the dephenolizer, if it is ydesired to increasethe percentage of conversion of the solutionin` the tank a portion of it maybe withdrawn through pipe to the tank 45` and there mixed with '080 fresh caustic to be Vreturned tothe absorbingsys.-

tem as described hereinabove.

Phenolate solution is discharged from tank 7 through a pipe 116 by air introduced underv prssure through a pipe 118, orby a pumpforl other (g5 suitable means, for 'recovery of phenols or other disposal. The `tank should also be provided with aventl19.`

l Itis to beV understood that in the foregoing vdescription vthe 4term ,phenols is synonymous with tar acids and includes phenol, cresol, and" their homologues. Similarly dephenolization signies the removal of' these tar acids; dephey nolizer, the` apparatus in whichsuch' removal is practiced; and phenolate the saltsof these acids.` ff v Y Furthermore, althoughk our process has been described in connection with the removal of tar acids Afrom lammoniacal gas liquor it is not 4limited to that application, but is broadly adaptedr lto the treatment of any liquid containing tar acid. f y

It will be obvious to those skilledlinlthe artiA that Vvarious `rnodiiications can be made'in ythe several parts of our apparatusand the several steps of ourjprocess in addition to tho'seenurner ated hereinabove without departing from" the spirit of our invention, and it is our intention included within the scop'etliereof." Y

` We claim as` our invention?V tar acid which comprises `recirculating VVgasy throughsaid `liquid and through an absorbent' purities by chemically combining vsaid'ir'nizsurities to form substantially insoluble compounds-` 2. The processv of treating aliquid containing tar acidand normally gaseous acidic 'impurities'v which comprises recirculatingggas through said 120 liquid and through an' alkaline absorbent for tar acids, and preventing vcontamination of the said alkaline absorbent with acidicV impurities by chemically combining said Y impurities lto formr compounds insoluble in the said absorbent.

3. The process of treating a liquid containing tar acid and carbon dioxide whichA comprises recirculating gas through said liquid and through ing' the carbonation of the saidl alkaline absorbent by chemically combining said carbon dioxide' to form a substantially insoluble compound.

` 4. The process of treating a liquidcontaining tar acid which comprises recirculating an` inert gas through said liquid and through an absurbel Vent for -tar acids in a system maintained at a temperature near the boiling pointV ofthe said `liquid, and preventing ab'sorptionof carbon dix-f ide by the said yabsorbent by chemically combining insoluble compound having substantially no vapor pressure with respect to carbondioxide. n

5. The process vof treating fan aqueous liquid containing tar acid which comprises recirculating gas through a system including a stripping stage wherein theY saidV gas removes tar acid ,fromV the saidliquid and `through.an absorbing stage wherein tar acid is absorbed Vfrcirnwthe recirculat` ing gas byanalkaline solution, and contacting carbon dioxideentering `the said system with,V a

, ri'o f lfThe process of treating a' liquid containing 6 fixing agent with Vwhich the carbon dioxide reactsto form an insoluble compound, whereby carbonationgof the said alkaline solution is preventtarA acid which comprises recirculating hot lgas ingsystem wherein thesaid gas transfers tar acid from the said liquid to an alkaline absorbent fortaracida and preventing carbonation of the said alkaline absorbent with carbon dioxide enteringthe system in volatile form asa constituent of said liquid by causing said carbon dioxide to react with a calcium compound to form cal-Vr ciurncarbonata 8. Ina process of transferring tar acid from an aqueous liquid containing it. and free carbon Y dioxide to an alkalineabsorbent for taracids by Y dioxide to an alkaline absorbent fortar yacids by `a current of hot gas, the method of vpreventing carbonation of the said alkaline absorbent which comprises adding to the said liquid a fixing agent with which the said carbon dioxide reacts to form aninsolublecompound. i Y Y 9. Ina process of transferringtar acidA from an aqueous liquid containing-it and free carbon a current of hot gas,`the method of preventing vcarbonation ofthe said alkaline absorbent which comprises adding to the said liquid ammonia-still wastefcontaining a sufficient quantity of calcium saltstocombine with the said carbon dioxide to form calcium carbonate.

10. In al process. of transferring tar acid from an aqueous liquid Ato an alkaline absorbent for tar acids by a current of gas, the method of preventing carbonation of saidv alkaline absorbent with carbon dioxide contained in said gas which comprises removing carbon dioxide from said gas by chemically combining the said carbon'dioxide with a fixing agent with which the gas is kcontacted. i

l1. vThe process of treating a liquid containing tar acidA which comprises passing gas through the said liquid and through an alkaline absorbent for tar acids containing a fixing agent which reacts with carbon dioxide to form an insoluble carbonate. f

Y12. The process of. treating a liquid containing tar acid which comprises contacting gas with a fixing agent which reacts with carbon dioxide vto form an insoluble compound having substantially no vapor pressure with respect to carbon dioxide, and recirculating the said gas through a systemin which itl removes tar acid from `the saidV liquid and transfers the removed tar acid to an alkaline absorbent.

' 13. The'process of treating a liquid containing tar acid and carbon dioxide which comprises adding to the said liquid a fixing agent'which reacts with thesaid carbon dioxidev to form an insoluble compound, filtering the liquidto re move rsolids therefrom, and recirculating gas through the filtered liquid and through an alkaline absorbent for tar acids at a temperature L near the boiling point of the liquid.

14. The A.process ofY treating ammoniacal gas liquorvcontaining tar acid and carbondioxide which comprises recirculating hot gas saturated with water vapor through said liquor and through lan alkaline absorbent'for tar acids, whereby tar said absorbent, and chemically combining; the carbon dioxide with a fixing agent to form an insoluble compound,` whereby carbonation of the said absorbent is. prevented. .f Y l5. The process of `transferring tar acid from an aqueous liquid containing it to an alkaliney absorbent for tar acids, which comprises recirculating gas through a stripping stage wherein it removes tar acid from the said liquid and through an absorbing stage wherein the recirculatedgas is purified from tar acid by an alkaline solution, said solution being supplied Vintermittentlyto a section of the absorbing stage and recirculated `over anothersection. of said stage countercur rently with the iiow of recirculated. gastherethrough.

15. The process of removing tar acid from gas which comprises contacting theY gas with a yrecirculated alkaline absorbent for tar acids ,wher'e by tar acid ispartially removed from the gas, and then contacting the gas with" intermittently supplied fresh absorbent. L

17. The process of removing tar acid vfrom gas which comprises contacting the gas with ,a resupplied relatively uncontaminated alkaline solu tion, adding the latter solutionv to the recirculating solution;l withdrawing excess lrecirculating solution, mixing the withdrawn solution with substantially freshalkaline solution, and intermittently returning portions'of' the resulting mixed solution into contact with the gas.

' 19. The process of removing tar acid from gas which comprises contacting the. gas withv an alkaline solution which absorbs tar acid, thereby forming alkali phenolate in the solution' and purifying the gas, withdrawing the solution from contact with the gas, mixing fresh alkaline solution with the withdrawn solution, and intermittently supplying the. resulting mixed'solution to the system to remove tar acidr from a further quantity of gas. 1

20. The process.l of treating ammoniacal gas liquor containing tar acid vand carbon dioxide,

acidl is transferred from the said liquor tothe whichcomprises distilling the liquor to remove FREDERICK w. sPERR, JR. JOSEPH A. SHAW. 

